DE102004009821A1 - Method of operating a steering system with configuration of useful applications - Google Patents

Abstract

A method for operating a steering system for a motor vehicle with at least one steerable wheel, an actuator and a superposition gearbox, wherein by the superposition gear initiated by the driver of the vehicle steering movement and initiated by the actuator movement for generating the steering movement of the steerable wheel for the realization of Useful applications are superimposed on a pinion angle, wherein the actuator is driven to initiate the movement by a control signal of a control unit and the control unit for determining the control signal receives the steering wheel angle, the pinion angle and other vehicle-specific parameters, in particular a vehicle speed, as input signals. Input signals of the control unit are checked for plausibility, in particular by means of safety functions of a safety monitoring method, and the useful applications of the steering system are configured on the basis of the results.

Description

The The invention relates to a method for operating a steering system according to the preamble of claim 1.

A generic method is from the DE 197 51 125 A1 known. In this case, the steering movements applied by the driver through a steering wheel, the steering wheel angle detected by a sensor, are superimposed by means of an overlay gear with the movements of the actuator, the motor angle. The resulting superimposed movement is forwarded via the steering gear or the steering linkage to the steerable designed wheels for adjusting the steering angle. Here, the actuator is designed as an electric motor. The operating principle or the useful applications of such a power steering system are, in particular, that the steering can be performed indirectly by the translation of the superposition gearing and thus low steering wheel torque can be achieved. As a result, very large steering wheel angles are avoided by superimposing suitable motor angles so that output angles required with steering wheel angles of conventional size can be set. The required for steering assistance motor angle or its target value is determined from the steering wheel angle. In addition, the motor angle may also be dependent on signals which by sensors and / or other vehicle systems, such as. B. represent an electronic stability program (ESP) detected vehicle movements. This is done by a control unit, on which the programs necessary for the determination of the required motor angles or for the control of the useful applications are executed.

by virtue of the safety requirements for such a steering system, is a Safety concept with safety and diagnostic functions, in particular around random Errors in the sensors, the control unit itself or the actuators to discover and react appropriately, d. H. for example the Useful applications, in particular the variable steering ratio suitable to switch and / or start appropriate replacement modes, essential. The input signals of the control unit are checked for plausibility. For example would it be adversely an adulterated Speed signal to accept, because the variable steering ratio depending on speed is varied.

Of the The present invention is therefore based on the object, a method to provide for the operation of a steering system, of the type mentioned, which high security through reliable switching of the application guaranteed.

According to the invention this Problem solved by the characterizing part of claim 1.

By these measures becomes the method according to the invention extended to operate a steering system in an advantageous manner. This is the plausibility the input data of the controller continuously monitored by means of suitable safety functions and because of the surveillance the payload applications (eg variable steering ratio) are configured switched accordingly. As a result, both a fallback level of the useful applications (steering assistance functions) for faulty input signals as well as a re-entry into their normal operating modes (all inputs can reused). In particular, this is the Availability of the steering system increases.

Advantageous It is when to configure the utility replacement modes and Switching conditions are specified.

If for example, no reliable Data regarding the speed of the motor vehicle exist, Thus, if there is a switchover condition, appropriate Replacement modes for the variable steering ratio be switched. Especially at higher speeds be too low steering wheel torque or too direct translation disadvantageous can (eg when driving on the highway).

The Presetting the replacement modes and switching conditions are in more advantageous Way implemented by a state machine.

When Nutzanwendung is a variable steering ratio into consideration. Of others are obvious Other uses conceivable.

In a procedural embodiment of the Invention may also be provided that the variable steering ratio at least based on the input data steering wheel angle, pinion angle and Vehicle speed is configured.

Consequently are the essential safety-related input data of the variable steering ratio involved in the configuration, ensuring high security is achieved.

Advantageous is, if in the presence of a faulty input signal, a predefined steady replacement signal is used and / or again plausible been switched input signal to this again steadily becomes.

Discontinuities in the set target engine angles can be avoided by who the. Safe predefined substitute signals are approached steadily or smoothly for the erroneous signals, and conversely, if the current input signals are plausible again, they are also smoothly approached again. For this purpose, steady setpoint values for the motor control could be generated in advance, to which then appropriate recourse is made.

following is an embodiment of the invention with reference to the drawing described in principle.

It demonstrate:

1 and 2 a schematic of the steering system according to the prior art, from which the invention proceeds in the embodiment; and

3 a schematic of a state machine for configuring a variable steering ratio.

in the The following is intended to illustrate the invention with reference to an embodiment become. This is exemplified by an overlay steering mentioned above went out.

The 1 respectively. 2 shows by the reference numerals 11 respectively. 21 an operable by the driver of the vehicle steering wheel. By the operation of the steering wheel 11 respectively. 21 becomes a superposition gearbox 12 respectively. 22 over a connection 101 a steering wheel angle δ _S supplied. At the same time the superposition gearbox 12 respectively. 22 over a connection 104 a motor angle δ _{M of} an actuator 13 respectively. 23 supplied, wherein the actuator may be designed as an electric motor. Output side of the superposition gearbox 12 respectively. 22 becomes the superimposed motion or the pinion angle δ _G via a connection 102 . 103 a steering gear 14 respectively. 24 fed in turn via a steering linkage 16 according to the superimposed motion or the total angle δ _G steerable wheels 15a and 15b with a steering angle δ _Fm acted upon. The mechanical translation of the superposition gearbox 12 respectively. 22 for δ _M = 0 with i _Ü = δ _G / δ _S and the mechanical transmission of the steering gear 14 respectively. 24 denoted by the reference i _L.

On the steerable designed wheels 15a and 15b acts a influenced by the road reaction moment M _V. In the 2 are still sensors 26 and 28 to see, with the sensor 28 the steering wheel angle δ _S detected and a control unit 27 feeds while with the reference numeral 26 Sensors are detected, which detect the movements of the vehicle (eg yawing, lateral acceleration, wheel speeds, vehicle speed v _X , etc.) and corresponding signals to the control unit 27 respectively. The control unit 27 determined, depending on the detected steering wheel angle δ _S and possibly depending on the vehicle movements a manipulated variable u to control the actuator 13 respectively. 23 for the realization of useful applications (eg variable steering ratio). The signals of the sensors 26 can also be taken from a CAN bus system of the vehicle.

Between the in the 1 respectively. 2 represented angles and torques apply the known relationships (i _L () is a non-linear function): i L (δ fm ) = [δ S / i Ü + δ M ] (1) and M L = M V / (I L · i Ü ) (2)

A power steering function is by the in the 1 and 2 shown steering system achieved in that by a large overall ratio (i _L · i _Ü ), ie by a very indirect steering, the steering wheel torque M _{L is} reduced. The steering wheel angle δ _S is superimposed on a motor angle δ _M according to the above equation 1, so that a desired front wheel angle δ _Fm can be adjusted with a not too large steering wheel angle δ _S. In this case, connections between the steering wheel angle δ _S and the steering angle δ _Fm can be realized by a suitable control of the engine, which can also depend on the driving state, for example the vehicle speed v _X or the steering wheel angle δ _S.

According to the above equation 2, the steering wheel torque M _{L is} only dependent on the reaction torque M _V at the steerable wheels and thus can not be influenced by the engine intervention. This results in the already mentioned problem that can not be achieved for all driving conditions acceptable steering wheel torque or steering feel by choosing a constant ratio of the steering gear. In particular, the steering wheel torque M _L should not be too large in the stand at large steering angles, while it may not be too small when driving at high speed.

Due to the resulting safety requirements for the steering system, is a safety concept with safety and diagnostic functions, in particular, to random errors in the sensors 26 . 28 , the Steuerge advises 27 itself or the actuators to detect and respond appropriately, ie, for example, the useful applications, in particular the variable steering ratio suitable to switch and / or to start appropriate replacement modes, essential. The input signals of the controller 27 , in particular δ _S and the vehicle-specific data of the sensors 26 , are checked for plausibility. For example, it would be disadvantageous to have a wrong Ge speed signal v _{X of} the vehicle to accept, since the variable steering ratio is varied depending on the speed.

In 3 is a state machine with states and transitions for the configuration of a variable steering ratio, ie to switch these suitable and to transfer to corresponding alternative modes / states shown. This is called a computer program on the control unit 27 Implemented method used to operate the steering system as part of a safety monitoring process.

In addition to the standard states "off", "reset" and "nominal" (default), more are defined. The nominal state "nominal" uses as inputs the steering wheel angle δ _S , the pinion angle δ _G and the vehicle speed v _X. If one or more of these input signals is / are faulty (can be detected via safety functions), suitable alternative states are switched. These are "without δ _S ", "without δ _G ", "without v _X " and "without δ _G and v _X ". In addition, how is out 3 As can be seen, a "constant" state is provided for development purposes.

If several errors should occur at the same time, the error state "without δ _S " is classified as most relevant and given the highest priority, because then it is not even known in which direction the driver would like to steer at all.

The Initialization of the state machine always takes place at the entrance.

A-Transitions A1 to A3 indicate the default route from input via "reset" to "nominal" and finally to "off". B-Transitions B1 to B5 describe a switch to the development mode "constant" and back. C-transitions C1 to C3 degrade the "nominal" state while D-transitions D1 to D5 switch between different fault states. E-transitions E1 to E4 finally return the error states "without δ _S ", "without δ _G ", "without v _X " and "without δ _G and v _X " to the "reset" mode.

• – A1: Die Funktion (variable Lenkübersetzung) wurde nicht durch eine übergeordnete Statusmaschine ausgeschaltet;
• – A2: immer;
• – A3: Die Funktion wurde durch eine übergeordnete Statusmaschine ausgeschaltet;
• – B1: Die Funktion wurde durch eine übergeordnete Statusmaschine in den "constant"-Modus geschaltet;
• – B2: Die Funktion wurde durch eine übergeordnete Statusmaschine geschaltet und alle drei Signalzustände δ_S, δ_G und v_X sind in Ordnung;
• – B3: Die Funktion wurde durch eine übergeordnete Statusmaschine geschaltet und der Signalzustand δ_S ist in Ordnung;
• – B4: Die Funktion wurde durch eine übergeordnete Statusmaschine geschaltet und der Signalzustand δ_G ist in Ordnung;
• – B5: Die Funktion wurde durch eine übergeordnete Statusmaschine geschaltet und der Signalzustand v_X ist in Ordnung;
• – C1: Signalzustand δ_S ist nicht in Ordnung;
• – C2: Signalzustand v_X ist nicht in Ordnung;
• – C3: Signalzustand δ_G ist nicht in Ordnung;
• – D1: Signalzustand δ_S ist nicht in Ordnung;
• – D2: Signalzustand δ_G ist nicht in Ordnung;
• – D3: Signalzustand δ_S ist nicht in Ordnung;
• – D4: Signalzustand v_X ist nicht in Ordnung;
• – D5: Signalzustand δ_S ist nicht in Ordnung;
• – E1: alle drei Signalzustände δ_S, δ_G und v_X sind in Ordnung;
• – E2: alle drei Signalzustände δ_S, δ_G und v_X sind in Ordnung;
• – E3: alle drei Signalzustände δ_S, δ_G und v_X sind in Ordnung; und
• – E4: alle drei Signalzustände δ_S, δ_G und v_X sind in Ordnung.

The transitions will be delivered under the following conditions:

• A1: the function (variable steering ratio) has not been switched off by a superordinate state machine;
• - A2: always;
• A3: The function was switched off by a higher-level status machine;
• B1: The function was switched to the "constant" mode by a superordinate state machine;
• B2: The function was switched by a higher-level state machine and all three signal states δ _S , δ _G and v _X are in order;
• B3: The function has been switched by a superordinate state machine and the signal state δ _S is in order;
• B4: the function has been switched by a superordinate state machine and the signal state δ _G is in order;
• B5: The function was switched by a higher-level state machine and the signal state v _X is OK;
• C1: signal state δ _S is not correct;
• - C2: signal state v _X is out of order;
• - C3: signal state δ _G is out of order;
• D1: signal state δ _S is not correct;
• - D2: signal state δ _G is out of order;
• - D3: signal state δ _S is out of order;
• - D4: signal state v _X is out of order;
• - D5: signal state δ _S is not correct;
• E1: all three signal states δ _S , δ _G and v _X are OK;
• - E2: all three signal states δ _S , δ _G and v _X are OK;
• E3: all three signal states δ _S , δ _G and v _X are OK; and
• - E4: all three signal states δ _S , δ _G and v _X are OK.

transition B1 has priority across from A2. A1> C1> C2> C3 is the priority when the "nominal" state is left. B3> B4> B5 are the priorities when leave the "constant" state (the remaining conditions are mutually exclusive). The transition D1 has priority over D2. The transition D3 has priority across from D4 (E2 is independent of these).

In further embodiments could also Alternatively states such as "low vehicle electrical system voltage", "without yaw rate", "without longitudinal acceleration" and / or "without lateral acceleration" along with associated transitions considered in the state machine if these input signals are relevant.

Also could in a further embodiment be provided that in the presence of a faulty input signal a predefined steady replacement signal is used and / or with again become plausible input signal on this again is switched constantly. As a result, discontinuities in the To be set target engine angles avoided. Safe predefined Replacement signals are for the faulty signals are smoothly approached and vice versa with renewed plausibility the current input signals, these also started again smoothly. Could do this in advance, steady setpoints for the motor control are generated, which then resorted to accordingly becomes.

11

steering wheel

12

Superposition gear

13

actuator

14

steering gear

15a

bikes

15b

bikes

16

steering linkage

21

steering wheel

22

Superposition gear

23

actuator

24

steering gear

25

26

sensors

27

control unit

28

sensors

101

connection

102

connection

103

connection

104

connection

δ _S

steering wheel angle

δ _M

motor angle

δ _G

pinion angle

δ _Fm

steering angle

v _X

vehicle speed

i _ü

mech. translation of the superposition gearbox

i _L

mech. translation of the steering gear

M _V

Kickback

M _L

steering wheel torque

A1-A3

transitions

B1-B5

transitions

C1-C3

transitions

D1-D5

transitions

E1-E4

transitions

"Off"

Off state

"Reset"

Restore state

"nominal"

standard state

"Constant"

developmental state

"without δ _G "

Condition "without pinion angle"

"without δ _S "

Condition "without steering wheel angle"

"without v _X "

Condition "without vehicle speed"

"without δ _S and v _X "

Condition "without steering wheel angle and Vehicle speed "

Claims (8)

Method for operating a steering system for a motor vehicle with at least one steerable wheel ( 15 ), an actuator ( 13 ; 23 ) and a superposition gear ( 12 ; 22 ), whereby by the superposition gear ( 12 ; 22 ) initiated by the driver of the vehicle steering movement (δ _S ) and by the actuator ( 13 ; 23 ) initiated movement (δ _M ) for generating the steering movement of the steerable wheel (δ _Fm ) for the realization of useful applications in a pinion angle (δ _G ) are superimposed, wherein - the actuator ( 13 ; 23 ) for initiating the movement (δ _M ) by a control signal (u) of a control unit ( 27 ) is controlled and - the control unit ( 27 ) for determining the control signal (u) receives the steering wheel angle (δ _S ), the pinion angle (δ _G ) and further vehicle-specific parameters, in particular a vehicle speed (v _X ) as input signals, characterized in that the input signals (v _X , δ _G , δ _S ) of the control unit ( 27 ), in particular by means of safety functions of a safety monitoring system, are checked for plausibility and the results are used to configure the useful applications of the steering system. Method according to claim 1, characterized in that for the configuration of the payload applications, replacement modes and switchover conditions be specified. Method according to claim 2, characterized in that that the specification of the replacement modes and switching conditions by a State machine is implemented. Method according to claim 1, 2 or 3, characterized that as a Nutzanwendung a variable steering ratio is used. A method according to claim 4, characterized in that the variable steering ratio is at least on the basis of the input signals steering wheel angle (δ _S ), pinion angle (δ _G ) and vehicle speed (v _X ) is configured. Method according to one of claims 1 to 5, characterized in the presence of a faulty input signal, a predefined steady replacement signal is used and / or again plausible been switched input signal to this again steadily becomes. Computer program with program code means for carrying out a method according to one of Claims 1 to 6, if the program is stored on a computer, in particular on the control unit ( 27 ) of the steering system is executed. Control unit ( 27 ) for a steering system for executing a computer program according to claim 7.